4.6 Watersheds

Watersheds: The land draining into a specific body of water (river, lake, bay, etc.)

• Defined by slopes; ridges divide watersheds affecting runoff directions

• Vegetation, soil composition, and slope affect drainage

• More vegetation = more infiltration (more space created by roots in soil) and groundwater recharge; less runoff

• Greater slope = faster runoff velocity and increased soil erosion

• Soil permeability influences runoff versus infiltration rates

Human Activities Impacting Water Quality

• Agriculture, clearcutting, urbanization, dams, mining, etc.

Chesapeake Bay Watershed

• Drains into streams/rivers, ends in Chesapeake Bay

• Mix of fresh & saltwater + nutrients creates productive estuary habitats

Estuary & Wetlands Provide Ecosystem Services

• Tourism revenue: hotels, restaurants, permits

• Water filtration: grass roots trap pollutants

• Habitats for food sources: fish & crabs

• Storm protection: absorbs and buffers floods

Human Impacts on Chesapeake Bay

• Nutrient pollution (N & P) causes eutrophication

• Algae bloom → decreased sunlight → dying plants → bacteria decompose → hypoxia (low O2) & dead zones

Major N & P Sources

• Sewage treatment plant discharge

• Animal waste from CAFOs

• Synthetic fertilizer runoff from fields & lawns

Other Major Pollutants

• Endocrine disruptors (from sewage)

• Sediment pollution (deforestation, urbanization, AG runoff), increases turbidity

Effects of Clearcutting on Watersheds

• Soil Erosion: Loss of vegetation leads to sediment in waterways, warming water, increasing turbidity

• Increased Soil & Stream Temperature: Loss of vegetation increases temperatures by reducing tree shade and increasing sediment warming

Solutions to Watershed Pollutants

• Implementing buffer strips of vegetation along streams to filter pollutants

• Promoting sustainable forestry practices that minimize clearcutting

• Restoring native vegetation in areas affected by clearcutting to stabilize soil and maintain temperature regulation